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Is it possible to add a password to an existing zipfile with 7zip without going to all the trouble of unpacking it and re-packing it again?

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What platform (Linux, Windows, ...) are you using? – whitequark Nov 25 '10 at 2:14
@Dennis: well, if you are writing this seriously, it's sad, and if not, it's not funny anyway. (And what if I'd say that regular 7zip executable won't run on Windows 3.11?) – whitequark Nov 25 '10 at 3:07
I run windows 7 and ubuntu linux 10.10, depending on what needs doing. 7zip is cross platform though so what difference does that make? – matt wilkie Nov 25 '10 at 16:33
up vote 2 down vote accepted

You can password-protect an existing ZIP file with zipcloak.

EDIT: T. Furukawa crafted a patch for zipcloak that adds a password option, so batch processing is much easier: C:\>for %f in (*.zip) do zipcloak -p password %f.

If you prefer a GUI, both WinRAR and PeaZip can batch encrypt existing archives.

  • In WinRAR: Select ZIP files > Tools > Convert archives > Compression... > Set password...

  • In PeaZip: Select ZIP files > Convert > Enter password / keyfile (optionally set algorithm to ZipCrypto under the Advanced tab for compatibility with Windows' built-in ZIP handling)

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By nature if you want the file to be encrypted, it needs to be unpacked and repacked, since the whole archive needs to be encrypted with the password.

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That's the correct answer ;) - Even if a program gives you an option to add a password to a ZIP file in one single step it will internally repack all files. – BlaM Nov 27 '10 at 15:27
@BlaM thanks for the clarification. Though thinking about it more carefully, the "going to all the trouble" bit is really about avoiding my trouble, not the computer's. ;-) So I'd be okay with that option, which doesn't seem to available anyway. – matt wilkie Nov 29 '10 at 0:20

Would it work for you to zip the zip file? Use no/low compression and encrypt the original zip file. Its a lot quicker than repacking the original files.

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